class ListMetaclass(type):
    def __new__(cls,name,bases,attrs):
        attrs['add']=lambda self,value:self.append(value)
        
        return type.__new__(cls,name,bases,attrs)
class Mylist(list):
    __metaclass__=ListMetaclass
'''
L=Mylist()
L.add(1)
L
[1]
L.add(2)
L
[1, 2]
'''